In a typical network environment, a switch may be utilized to facilitate communications between various segments of a single network, or between distinct and separate networks, in an intelligent and accordingly efficient manner. Specifically, a switch may in time learn the network addresses of the various network devices on network segments, or distinct networks, coupled to the respective ports of the switch by respective wires. Such wires may include copper wires in the form of twisted-pair wires or co-axial cables. The wires may furthermore be classified as comprising Category 1-5 wiring according to the EIA/TIA 568 specification. By examining each packet received at the switch, the switch is able to make a determination as to whether the received packet should be propagated out of a particular port, and over a particular segment or network, based on the destination address information associated with the received packet.
FIG. 1 illustrates an exemplary packet switching environment 1010 in which packet communication between three distinct networks, namely networks 1014, 1016, and 1018, is facilitated by a switch 1012. Of course, the switch 1012 to may include any number of ports, and made thus couple any number of networks. The network 1014 is coupled to a port 1020 of the switch 1012 by a wire 1022, the network 1016 is coupled to a port 1024 by a wire 1026, and the network 1018 is coupled to the port 1028 by the wire 1030. Each of the ports 1020, 1024 and 1028 is coupled to a switch core 1032 (also known as a "switch fabric") through which packets are propagated or routed between the ports. The switch core 1032 is shown to be coupled to a memory resource in the form of a Dynamic Random Access Memory (DRAM) 1034, which provides a buffer resource to the switch core 1032. All valid packets received at the switch core 1032 are propagated to the DRAM 1034 on a bus 1035 coupling the DRAM 1034 and the switch core 1032. An address lookup device 1036 is shown to snoop the bus 1035 for the purpose of learning address information, and constructing an address lookup table mapping network device addresses to ports of the switch 1012.
In the packet switching environment 1010 illustrated in FIG. 1, the wires 1026 and 1030 are shown to be physically distant from each other. Accordingly, a packet transmission 1038 between the networks 1014 and 1016 may occur without generating any cross-talk on the wire 1030. FIG. 2, on the other hand, illustrates an alternate packet switching environment 1040 in which the wires 1026 and 1030 are bundled together in a common cable 1342. In such a situation, so-called "near end" cross-talk (or signal leakage) may occur between the wires 1026 and 1030. The cross-talk is most likely to occur in close proximity to the ports 1024 and 1028 when a packet is being transmitted from one of these ports, while the other is listening on its respective wire. Consider, for example, the transmission of a packet from the network 1014 to the network 1016, as indicated at 1044. As the packet is transmitted from the port 1024, the signal strength is at a maximum. As the wire 1026 is brought into close proximity with the wire 1030 while propagating a high-powered transmit signal, there is a possibility that a cross-talk signal may be generated, as indicated at 1046, on the wire 1030. A receiver of the port 1028 may be in a state of maximum sensitivity for the purposes of reception, and accordingly the cross-talk signal may be received at the port 1028, and routed to the switch core 1032. As the address lookup device 1036 may have previously learned the source address of a packet, embodied by the cross-talk signal, as being associated with a device on the network 1014, an incorrect modification to an address lookup table may occur. Specifically, the address lookup device 1036 may indicate the source address of the cross-talk signal as belonging to a device on the network 1018. This may in turn result in packet switching errors.
The above identified problem discussed with reference to FIG. 2 may be exacerbated when the wires 1026 and 1030 are not well insulated. For example, where the wires 1026 and 1030 comprise Unshielded Twisted Pair (UTP) wires of Category 1, the possibility for the generation of cross-talk signals may be increased. Further, in certain networking environments, the frequency and power levels of transmit signals may increase susceptibility of the network to wire cross-talk.